statistical analysis
The program SPSS version 16 was used to analyze the data collected. Prior to analysis, normality tests were done for all continuous data, after which the appropriate statistical tools were selected. Descriptive statistics, which included mean, median, standard deviation, geometric mean, and frequency, were used. Chi-square tests (χ2) were used to compare the categorical data obtained from participant groups. Because the urinary metabolite concentrations were highly skewed, the concentrations below the limit of detection (LOD) were assigned a value equal to LOD/√2, as recommended by the Centers for Disease Control and Prevention (CDC),
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